Interaction of lp-dlg/KIAA0583, a membrane-associated guanylate kinase family protein, with vinexin and β-catenin at sites of cell-cell contact

Vinexin is a recently identified cytoskeletal protein and plays a key role in the regulation of cytoskeletal organization and signal transduction. Vinexin localizes at sites of cell- extracellular matrix adhesion in NIH3T3 fibroblasts and at sites of cell- cell contact in epithelial LLC- PK1 cells. Expression of vinexin promotes the formation of actin stress fiber, but the role of vinexin at sites of cell- cell contact is unclear. Here we identified lp- dlg/ KIAA0583 as a novel binding partner for vinexin by using yeast two- hybrid screening. lp- dlg/ KIAA0583 has a NH2- terminal coiled- coil- like domain, in addition to four PDZ domains, an Src homology ( SH) 3 domain, and a guanylate kinase domain, which are conserved structures in membrane- associated guanylate kinase family proteins. The third SH3 domain of vinexin bound to the region between the second and third PDZ domain of lp- dlg, which contains a proline- rich sequence. lp- dlg colocalized with vinexin at sites of cell- cell contact in LLC- PK1 cells. Furthermore, lp- dlg colocalized with beta- catenin, a major adherens junction protein, in LLCPK1 cells. Co- immunoprecipitation experiments revealed that both endogenous and epitope- tagged deletion mutants of lp- dlg/ KIAA0583 associated with beta- catenin. We also showed that these three proteins could form a ternary complex. Together these findings suggest that lp- dlg/ KIAA0583 is a novel scaffolding protein that can link the vinexin- vinculin complex and beta- catenin at sites of cell- cell contact.